OK, so picture you are banking across the middle of the table to the side pocket you are standing near. You need to figure out a point at which to aim the object ball so it will bank into that pocket. So while you are looking at the table at the far bank that you will use to bank the ball, imagine the table was now twice as wide i.e. the far bank now twice as far away. Keeping that imaginary distance in mind, now find the spot on that imaginary bank that is halfway between your object ball and the side pocket in which you want the object ball to sink. Shoot the object ball at that imaginary point, and it will bounce off the right place on the real bank and into the side pocket. Provided you pictured everything correctly and didn’t put spin on the ball.
If it still isn’t clear, just ask about which part again.